1. Field of the Invention
The present invention relates to an image display device, and more particularly, to an image display device capable of displaying an expanded image signal when an image signal input to the device has a smaller number of pixels than the number of pixels of a display panel.
The present invention also relates to a driver circuit for use in a display device with a high-resolution display panel in which the resolution is switched during an operation.
2. Description of the Related Art
In image display devices for use in personal computers or the like, the number of pixels of a display panel is defined in various standards. Widely used standards include VGA, SGVA, XGA, SXGA, and UXGA. In these standards, the number of pixels per frame is defined as follows.
VGA: 640 pixels in the horizontal direction and 480 pixels in the vertical direction;
SVGA: 800 pixels in the horizontal direction and 600 pixels in the vertical direction;
XGA: 1024 pixels in the horizontal direction and 768 pixels in the vertical direction;
SXGA: 1280 pixels in the horizontal direction and 1024 pixels in the vertical direction; and
UXGA: 1600 pixels in the horizontal direction and 1200 pixels in the vertical direction.
(In the above description, VGA, SVGA, XGA, SXGA, and UXGA are all registered trademarks of IBM Corp.)
In some cases, it is required to display an image signal on a display device according to a standard which is different from that of the image signal such as when a VGA image signal is displayed on an XGA display panel. In such a case, it is required to expand a VGA image signal to a size corresponding to the size of the XGA high-resolution display panel.
Two conventional signal expansion techniques are known in the art of the image display device as described below.
A first technique is, as shown in FIG. 8, to switch the sampling frequency at which an analog-to-digital converter 101 converts an analog signal to a digital signal.
For example, when an analog signal such as that shown on the top of FIG. 9 is given, if the analog signal is sampled in response to a clock signal 1 at a fixed frequency, then digital data 1 is obtained as denoted by A, B, C, D, E, F, G, . . . . If the same analog signal is sampled in response to a clock signal 2 at a higher frequency, then different digital data 2 is obtained as denoted by h, i, j, k, l, m, n, o, p, q, r, . . . The latter digital data 2 includes an increased number of data compared to the digital data 1 obtained using the clock 1. This means that the image signal is expanded.
The second technique is to detect the resolution of a given image signal and to set the expansion ratio to a value corresponding to the ratio of the resolution of the display panel to that of the given image. Each frame of image signal is expanded according to the above expansion ratio by means of interpolation using an arithmetic circuit.
For example, when a VGA image signal is converted to an XGA image signal, the required expansion ratio is 1.6. This expansion ratio may be achieved for example by converting five data to eight data. More specifically, eight data h, i, j, k, l, m, n, and o are produced by means of calculation from five original data A, B, C, D, and E as shown ion FIG. 10. The calculation may be performed using the following equations:
h=Axc3x971.0 for data h,
i=Axc3x970.3+Bxc3x970.2 for data i,
j=Bxc3x971.0 for data j,
k=Bxc3x970.1+Cxc3x970.4 for data k,
l=Cxc3x970.4+Dxc3x970.1 for data l,
m=Dxc3x971.0 for data m for data m,
xe2x80x83n=Dxc3x970.2+Exc3x970.3 for data n,
and
o=Exc3x971.0 for data o.
In the standards described above, each pixel usually consists of three dots representing red (R), blue (B), and green (G), respectively.
When images according to various standards are modified so as to fit them to the display panel, it is required to expand or reduce the image including characters or the like such that the expanded or reduced image is displayed over the fixed display area of the screen.
The following signal expansion techniques are known in the art of the display device.
In one technique, the resolution of given image data is detected using a detection circuit and an expansion ratio is set depending on the ratio of the resolution of the display panel to the detected resolution of the image data. One frame of image data is stored in a frame memory and two consecutive lines of image data are read at a time from the frame memory. The two lines of image are expanded according to the above expansion ratio by means of interpolation using an arithmetic circuit, and resultant image is displayed on the display panel.
In the structure in which pixels each consisting of three dots are arranged in a matrix fashion, original luminance data to be displayed on three dots in each line are expanded using the arithmetic circuit wherein luminance is weighted by predetermined factors. The resultant expanded luminance data is applied to dots of respective pixels so that an image expanded in the direction along the line is displayed on the display panel.
In the above-described techniques, data calculation and re-sampling are required. Besides, an additional memory is required. As a result, the circuit becomes greater in scale and thus it becomes difficult to achieve a small-sized display device and higher cost is required.
One technique of displaying an expanded image without using an additional memory is to employ a display device constructed as shown in FIG. 26, which will be further improved according to the present invention as will be described later.
The display device shown in FIG. 26 includes a thin-film transistor liquid crystal display panel 201 including source interconnection lines and gate interconnection lines extending in a matrix fashion, first horizontal driver 202 and a second horizontal driver 203 connected to the source interconnection lines of the display panel 201, a vertical driver 204 connected to the gate interconnection lines of the display panel 201, and a signal processing circuit 205 for controlling the drivers 202, 203, and 204.
The signal processing circuit 205 includes a sampling circuit 207 to which an image signal or an original data is input, a frequency divider 208 and a signal selection circuit 209 both connected to the sampling circuit 207, a horizontal control circuit 210 for controlling the horizontal drivers 202 and 203, and a vertical control circuit 211 for controlling the vertical driver 204. A clock generator 212 is connected to the signal processing circuit 205. The liquid crystal display panel 201 employed herein is assumed to be of the XGA type including 1024 pixels in the horizontal direction and 768 pixels in the vertical direction.
In the display device shown in FIG. 26, if original data or an image signal according to the VGA standard (at a clock frequency of 27.175 MHz) such as a signal H (ABCDE . . . ) shown in FIG. 27 is input to the signal processing circuit 205, the signal is input to the sampling circuit 207. In synchronization with a sampling clock signal at 40.28 MHz, the sampling circuit 207 produces converted data I (AABCCDEE . . . ) as shown in FIG. 27. The resultant converted data I is sent to the frequency divider 208. In the above operation, in order to convert the VGA image signal with 1H=640 data to an XGA signal with 1H=1024 data, it is required to increase the number of data by a factor of 1.6 and thus the sampling is performed at a sampling clock frequency of 40.28 MHz which is 1.6 times the original clock frequency of 27.175 MHz.
After that, the converted data is divided by the frequency divider 208 into odd-numbered signals and even-numbered signals. The odd-numbered signals ABCE, . . . , which are represented by J in FIG. 27, are supplied via the signal selection circuit 209 to the first horizontal driver 202. Similarly, the even-numbered signals ABCE, . . . , which are represented by K in FIG. 27, are supplied to the second horizontal driver 203.
The horizontal control circuit 210 controls the drivers 202 and 203 so that signals are supplied to the source interconnection lines of the liquid crystal display panel 201 alternately from the first horizontal driver 202 and the second horizontal driver 203 thereby allowing the liquid crystal display panel 201 designed to display XGA images to display data AABCCDEE . . . as shown in FIG. 27 (data L) and also as shown on the liquid crystal panel 201 in FIG. 26.
On the other hand, in the case where XGA image signal is input as original data, the image signal is directly sent to the frequency divider 208 as represented by Ixe2x80x2 in FIG. 26 without being passed through the sampling circuit 207, and is subjected to the same dividing process in the frequency divider 208 as that described above. The XGA image signal is divided by the signal selection circuit 209 into two parts and supplied to the liquid crystal display panel 201. The divided signals are combined together on the display panel 201, and thus an XGA image is displayed thereon.
As described above, by employing the circuit shown in FIG. 26, it is possible to convert an original VGA image signal to XGA image signal by means of re-sampling the original image signal. The resultant XGA image signal is supplied to the liquid crystal display panel 201 and thus an XGA image originated from the VGA image signal is displayed on the liquid crystal display device 201.
However, the both signal expanding techniques described above have their own problems.
In the first technique, when an image signal generated by a personal computer is input as original data, miss-sampling can occur due to the difference from an ordinary image signal. The miss-sampling can cause flicker which results in degradation in image quality. Another problem is that when sampling is not performed at maximum and minimum values of the waveform of a given analog signal, a reduction in contrast occurs.
The problem of the second technique is that original data is not perfectly preserved after conversion and degradation in image quality such as a reduction in contrast can occur. In the specific example shown in FIG. 10, four data A, B, D, and E of the original data A, B, C, D, and E are converted by multiplying them by a factor of 1.0 and thus these data are directly employed as the converted data h, j, m, and o, respectively. However, the original data C is dispersed into components of the converted data k and l, and thus the data C is not preserved in its original form after the conversion. Therefore, although the overall converted image will be similar to the original image, a loss can occur in some individual data as is the case for data C in this specific example. Such a loss of data can cause a reduction in contrast.
The circuit configuration shown in FIG. 26 requires an additional circuit for generating a clock signal at a frequency different from that of original data. This result in an increase in the scale of the circuit which makes it difficult to achieve a small-sized display device. Furthermore, the operation at a higher frequency results in an increase in power consumption. For example, if a signal processing circuit which needs power consumption of 250 mW at a normal frequency is operated at a higher frequency, the power consumption will increase to about 400 mW. Furthermore, in the sampling operation on digital data at a different frequency, it is needed to meet severe requirements in terms of the sampling setup time and hold time. These severe requirements can cause degradation in reliability of the display device and also degradation in image quality.
In view of the above, it is an object of the present invention to provide an image display device and a driver circuit for use in the image display device, capable of handling images in various formats with different resolutions, in an easy and highly reliable fashion.
According to an aspect of the present invention, to achieve the above object, there is provided an image display device including a display panel having predetermined numbers of pixels defined in horizontal and vertical directions, respectively, and an interpolated-data generation circuit for producing interpolated data in such a manner that when the number of pixels in the horizontal direction of the display panel is greater than the number of pixels in the horizontal direction of an image signal, a plurality of original image data of the image signal at original locations along one horizontal pixel line are directly stored at data storage locations closest to the corresponding original locations, and data for the remaining data storage locations are each calculated from two original image data at locations adjacent to the respective data storage locations and resultant data are stored in the respective remaining data storage locations.
In the image display device according to the present invention, the interpolated data generation circuit preferably generates interpolated data such that a plurality of original image data of the image signal at original locations are directly stored at data storage locations closest to the corresponding original locations, and data for the remaining data storage locations are given such that either one of two original image data at adjacent data storage locations are stored in the respective remaining data storage locations wherein the data at each remaining data storage location is switched between two original image data at adjacent data storage locations from one horizontal pixel line to another adjacent horizontal pixel line of the image signal. Alternatively, the interpolated data generation circuit may generate interpolated data such that data for the remaining data storage locations are given in such a manner that either one of two original image data at adjacent data storage locations are stored in the respective remaining data storage locations wherein the data at each remaining data storage location is switched every image frame between two original image data at adjacent data storage locations.
As can be seen from the above description, the most distinctive feature of the image display device according to the present invention is in that a plurality of original image data are directly stored, without being subjected to any process, at data storage locations closest to original data locations. The data for data storage locations remaining after storing the original image data are given in any one of the following three manners:
(1) The data for each remaining data storage location is calculated from two original data stored at locations adjacent to the remaining data storage location.
(2) Either one of two original data at locations adjacent to each remaining data storage location is employed wherein the two data are alternately employed from one horizontal pixel line to another adjacent line.
(3) Either one of two original data at locations adjacent to each remaining data storage location is employed wherein the two data are alternately employed from one image frame to another frame.
The calculation in (1) may be accomplished for example by multiplying two adjacent original image data by proper factors and then adding them together. In the second conventional technique described earlier, a loss of original data which occurs during the conversion process causes a reduction in contrast. When a signal is expanded, the number of data always becomes greater after conversion than the number of original data. Taking this fact into account, in the image display device according to the present invention, when an image signal is expanded, data storage locations are first assigned in an interpolated-data generation circuit, and then original data are directly stored at data storage locations closest to the respective original locations of the original data. At data storage locations remaining after storing the original data, either of two original data at locations adjacent to the respective remaining data storage locations or data calculated from two original data at locations adjacent to the respective remaining data storage locations are stored. In any case, the image display device according to the present invention does not encounter a loss of original data during the conversion and thus it is possible to display an expanded image on the display panel while maintaining the contrast at the same level as that of the original image without encountering degradation in image quality.
In the interpolated-data generation circuit, in the case where the data at data storage locations remaining after storing original data are given by the sums of original data at locations adjacent to the respective remaining data storage locations multiplied by proper factors, it is desirable that the factors be determined so that the difference between the maximum and minimum expansion ratios of the interpolated data to the corresponding original data becomes less than 25% of the maximum expansion ratio.
If the above requirement is met, the average brightness of the original image is maintained after the conversion.
The process of expanding an image signal in the horizontal direction has been described above for the case where the number of pixels in the horizontal direction of the display panel is greater than the number of pixels in the horizontal direction of the image signal. Expansion may also be performed in the vertical direction in a similar manner as described below.
That is, according to another aspect of the present invention, there is provided an image display device including a display panel having predetermined numbers of pixels defined in horizontal and vertical directions, respectively, and an interpolated-data generation circuit for producing interpolated data in such a manner that when the number of pixels in the vertical direction of the display panel is greater than the number of pixels in the vertical direction of an image signal, a plurality of original image data of the image signal at original locations along one vertical pixel column are directly stored at data storage locations closest to the corresponding original locations, and data for the remaining data storage locations are each calculated from two original image data at locations adjacent to the respective data storage locations and resultant data are stored in the respective remaining data storage locations.
As in the horizontal direction, the data for data storage locations remaining after storing the original image data may be given in any one of the following three manners: the data for data storage locations remaining after storing the original data are each calculated from two original image data at locations adjacent to the respective data storage locations and resultant data may be stored in the respective remaining data storage locations; either one of two original data at locations adjacent to each remaining data storage location is employed wherein the two data are alternately employed from one pixel location to another adjacent location along the vertical column; or either one of two original data at locations adjacent to each remaining data storage location is employed wherein the two data are alternately employed from one image frame to another image frame.
In the expansion in the vertical direction, as in the horizontal direction, if the factors are set such that the difference between the maximum and minimum expansion ratios of the image data obtained after the interpolation relative to the corresponding original image data becomes less than 25% of the maximum expansion ratio, then it becomes possible to maintain the average brightness of the image at the same level as that of the original image. In the present invention, the term xe2x80x9cone framexe2x80x9d is used to represent one complete image and the term xe2x80x9cone fieldxe2x80x9d is used to represent any one of a plurality of images which are parts of one frame.
According to another aspect of the present invention, there is provided a driver circuit for use in an image display device, comprising a display panel having predetermined numbers of pixels defined in horizontal and vertical directions, respectively; a pair of source drivers connected to the display panel, for supplying a horizontal image signal having the predetermined number of pixels in the horizontal direction to the display panel; image signal lines which divide a given image signal into two identical signals and transmit them to both source drivers; and a horizontal image signal control circuit for supplying a pair of sampling timing signals to the pair of source drivers, respectively, thereby making the respective source drivers generate horizontal image signals each having a smaller number of pixels in the horizontal direction than the predetermined number such that a horizontal image signal having the predetermined number of pixels in the horizontal direction is obtained when the horizontal image signals generated by the pair of source drivers are combined.
If the driver circuit configured in the above-described manner is employed, by adjusting the sampling timing signal it is possible to make the source drivers generate image signals which will be combined together on the display panel so that an image with a resolution well matched with the resolution of the display panel is displayed thereon, without requiring either an additional memory or an additional clock generator. This makes it possible to achieve a reduction in the size of the circuit and a reduction in power consumption. Furthermore, the reliability of the display device is improved.
According to still another aspect of the present invention, there is provided a driver circuit for use in an image display device, comprising a display panel having predetermined numbers of pixels defined in horizontal and vertical directions, respectively; a pair of source drivers connected to the display panel, for supplying a horizontal image signal having the predetermined number of pixels in the horizontal direction to the display panel; a signal selection circuit which generates two image signals by copying a given image signal when the given image signal has a smaller number of pixels in the horizontal direction than the predetermined number, or generates two image signals by dividing the given image signal into two parts when the given image signal has the predetermined number of pixels in the horizontal direction, and then transmitting the resultant copied or divided image signals to the respective source drivers; a resolution detecting circuit for determining on the basis of a synchronizing signal whether the given image signal has the predetermined number of pixels in the horizontal direction or a smaller number of pixels in the horizontal direction than the predetermined number and supplying a control signal to the signal selection circuit to indicate whether the signal selection circuit should output the copied image signals or divided image signals; a frequency divider for dividing the given image signal into two parts and supplying resultant divided image signals to the signal selection circuit; and a horizontal image signal control circuit for supplying a pair of sampling timing signals to the pair of source drivers, respectively, thereby making the respective source drivers generate horizontal image signals each having a smaller number of pixels in the horizontal direction than the predetermined number such that a horizontal image signal having the predetermined number of pixels in the horizontal direction is obtained when the horizontal image signals generated by the pair of source drivers are combined.
With the driver circuit configured in the above-described manner, even when the input image signal has a number of pixels in the horizontal direction greater than the number of pixels in the horizontal direction of the display panel or when the input image signal has a number of pixels in the horizontal direction smaller than the number of pixels in the horizontal direction of the display panel, it is possible to supply an image signal adjusted to have a number of pixels in the horizontal direction well matched with the number of pixels of the display panel by dividing or copying the image signal and then applying it to the sampling process whose timing is controlled depending on the conversion ratio from the number of pixels in the horizontal direction of an input image signal to the number of pixels in the horizontal direction of the display panel. In the above process, the horizontal image signal having the predetermined number of pixels in the horizontal direction is partly removed. Because any arbitrarily specified part of data may be removed, it is possible to handle any conversion ratio.
Thus, it is possible to make the source drivers generate image signals which will be combined together on the display panel so that an image with a resolution well matched with the resolution of the display panel is displayed thereon, without requiring either an additional memory or an additional clock generator. This makes it possible to achieve a reduction in the size of the circuit and a reduction in power consumption. Furthermore, the reliability of the display device is improved.
According to still another aspect of the present invention, there is provided a driver circuit for use in an image display device, comprising a display panel having predetermined numbers of pixels defined in horizontal and vertical directions, respectively; a source driver connected to the display panel, for supplying a horizontal image signal having the predetermined number of pixels in the horizontal direction to the display panel; an image signal line for sequentially transmitting image signals, obtained by copying a given image signal, to the source driver; and a horizontal image signal control circuit for sequentially supplying a pair of sampling timing signals to the source driver thereby making the source driver sequentially generate horizontal image signals each having a smaller number of pixels in the horizontal direction than the predetermined number.
Alternatively, the horizontal image signal control circuit may sequentially supply a pair of sampling timing signals to the source driver thereby making the source driver generate a horizontal image signal while removing some part of the given original image signal so that the resultant image signal has a reduced number of pixels in the horizontal direction compared to the original number wherein the data location at which data is removed from the given original image signal is varied at least every field, or every line, or every predetermined period of time.
By performing the signal processing in the above-described manner, it is possible to output an image with a resolution well matched with the resolution of the display panel without requiring either an additional memory or an additional clock generator. This makes it possible to achieve a reduction in the size of the circuit and a reduction in power consumption. Furthermore, the reliability of the display device is improved.
In order to produce a horizontal image signal having a smaller number of pixels in the horizontal direction than the predetermined number, the original signal has to be partly removed. However, it is possible to obtain an image similar to the original image by sequentially supplying the partly removed data to the display device or by supplying the partly removed data field by field or line by line or every predetermined period of time thereby averaging the partly removed parts over the entire screen. The partly removal of the data can be easily accomplished by temporarily stopping the clock signal to the source driver thereby temporarily stopping the sampling operation on the data.
According to still another aspect of the present invention, there is provided a driver circuit for use in an image display device, comprising a display panel having predetermined numbers of pixels defined in horizontal and vertical directions, respectively; a source driver connected to the display panel, for supplying a horizontal image signal having the predetermined number of pixels in the horizontal direction to the display panel; a signal selection circuit which generates two image signals by copying a given image signal when the given image signal has a smaller number of pixels in the horizontal direction than the predetermined number, or generates two image signals by dividing the given image signal into two parts when the given image signal has said predetermined number of pixels in the horizontal direction, and then sequentially transmitting the resultant copied or divided image signals to the source driver; a resolution detecting circuit for determining on the basis of a synchronizing signal whether the given image signal has the predetermined number of pixels in the horizontal direction or a smaller number of pixels in the horizontal direction than the predetermined number and supplying a control signal to the signal selection circuit to indicate whether the signal selection circuit should output the copied image signals or divided image signals; a frequency divider for dividing the given image signal into two parts and supplying resultant divided image signals to the signal selection circuit; and a horizontal image signal control circuit for sequentially supplying a pair of sampling timing signals to the source driver thereby making the source driver sequentially generate horizontal image signals each having a smaller number of pixels in the horizontal direction than the predetermined number such that a horizontal image signal having the predetermined number of pixels in the horizontal direction is obtained when the horizontal image signals sequentially generated by the source driver are combined.
Alternatively, the horizontal image signal control circuit may sequentially supply a pair of sampling timing signals to the source driver thereby making said source driver generate horizontal image signals while removing some part of the given original image signal so that the resultant image signal has a reduced number of pixels in the horizontal direction compared to the original number such that a horizontal image signal having the predetermined number of pixels in the horizontal direction is obtained when the horizontal image signals sequentially generated by the source driver are combined, wherein the data location at which data is removed from the given original image signal is varied at least every field, or every line, or every predetermined period of time.
In order to generate horizontal image signals having a smaller number of pixels in the horizontal direction than the predetermined number, which will be combined again into a single image having the above-described predetermined number of pixels, the original signal has to be partly removed. However, it is possible to obtain an image similar to the original image by sequentially supplying the partly removed data to the display device or by supplying the partly removed data field by field or line by line or every predetermined period of time thereby changing the locations where data are removed thus averaging the partly removed parts over the entire screen.